The present invention relates to a seat reclining device for a vehicle, which is provided to adjust a tilt angle of a seat back with respect to a seat cushion.
Conventionally, as such a seat reclining device for a vehicle, one described in, for example, Patent Document 1 is known. This seat reclining device for a vehicle includes an upper plate having an internal teeth portion, a lower plate pivotally supporting the upper plate, two pawls the radial movements of which are guided by two pairs of guide walls provided on the lower plate, a cam capable of contacting the radially-inner surfaces of these pawls, and two pressing members capable of contacting the corresponding inner surfaces of the pawls. The cam is capable of contacting the pressing members. Each pawl has external teeth capable of meshing with an internal teeth portion. The external teeth are urged by a spring, via the cam or via the cam and pressing members, in the direction in which these external teeth mesh with the corresponding internal teeth portion. Thus, the external teeth of the pawls are held to mesh with the corresponding internal teeth portions of the upper plate.
As shown in FIG. 7, a wedge-shaped space S is formed between the inner surface of a pawl 431, which is located between each pair of guide walls, and one guide wall 413 of each pair of guide walls. The pressing member 460 has a cylindrical shape and is located in the wedge-shaped space S. The pressing member 460 can be pressed from below in FIG. 7 by a cam (not shown). In this case, the pressing force F90 applied to the pawl 431 by the pressing member 460 is oriented substantially in a direction orthogonal to the tangent T90 of the pawl 431 at a pressing point P90, that is, in the direction of a normal line at the pressing point P90. Therefore, the pressing force F90 of the pressing member can be decomposed into a first component force F91 in the moving direction of the pawl and a second component force F92 in a direction orthogonal to the moving direction. The pawl 431 is pressed against the guide wall (not shown) opposite to the guide wall 413 mentioned above, and the gap between the pawl 431 and each guide wall can be filled by the pressing member 460. Thus, backlash of the seat is restricted. This results from the action of the second component force F92 holding the positions of the internal teeth of the upper plate against external force.
The second component force F92 acting on the pawl 431 increases with a decrease in the inclination angle θ in the acting direction of the second component force F92 with respect to the acting direction of the pressing force F90 (the direction of the normal line at the pressing point P90), that is, with a decrease in the inclination angle θ of the tangent T90 with respect to the moving direction of the pawl 431. Accordingly, backlash of the seat can be restricted more firmly.
However, as the second component force F92 acting on the pawl 431 increases, it becomes difficult to detach the pressing member 460 from the inner surface of the pawl 431. This is because the component force F94 of the frictional force F93 based on the pressing force F90 of the pressing member 460 acts to hinder disengagement of the pressing member 460 from the pawl 431, such that the component force F94 increases with a decrease in the inclination angle θ of the tangent T90 with respect to the moving direction of the pawl 431. In order to facilitate such disengagement of the pressing member 460 from the inner surface of the pawl 431, it may be proposed that the inclination angle θ of the tangent T90 with respect to the moving direction of the pawl 431 be increased. However, in this case, the second component force F92 onto the pawl 431 decreases, resulting in decrease in force holding the position of the internal teeth portion of the upper plate against external force, as described above.